Method of forming electrical lead-ins for fused quartz devices



May 16, 1933. w. 'r. ANDERSON, JR

METHOD OF FORMING ELECTRICAL LEAD-INS FOR FUSED QUARTZ DEVICES FiledMarch. 8, 1932 IN VEN TOR.

ATTONEY.

Patented Maf a, 1933 UNITED STATES PATENT OFFICE wnmuu 'r. mmsou, .13.,or NEWARK, NEW JERSEY, ASSIGNOB 'ro mom cannon. AND mammacruame comm, OFNEWARK, NEW JERSEY, A con.-

POBATION 01 NEW JERSEY m0!) 0] I'ORIING ELEGTRI IICAL LEAD-INS FOR FUSEDQUAIB J'Z DEVICES Application filed larch 8, 1932. Serial No. 597,460.

This invention relates to a method for constructing metallic electricalconductors for use in connection with gas tight fused quartz devices.

The introduction of metallic electrical conductors into vitreousevacuated and gas-filled systems has always been a problem. If thevitreous materials used are glasses, it has been found practical to sealthe metallic con-- ductor directly into the glass and to obtain a vacuumand gas tight seal provided the lass fused at a temperature lower thanthe %using temperature for the metal; and provided that the coeflicientof thermal expansion of the glass was the same or practically the sameas that of the metal. These requirements for the gas tight introductionof metal 4 conductors into glass are well known to the art and arefreely discussed and described in publications (see for example,Laboratory Glass Blowin F, O. Frary, C. S. Taylor & J. D. Edwards, 2ndedition, McGraw Hill Book Company 1928);

Many attempts have been made to seal'metallic conductors into fusedquartz for the production and attainment of a gas tight seal.

However, numerous'difficulties have been encountered. For example, fusedquartz has an extremely small coefiicient of thermal expansion, 0.6x10,and an alloy of nickel and iron, known as Invar, has a coefficient ofthermal expansion approximating this value,

and might possibly be fused into quartz to make a gas tight seal if itwere not for the fact that the Invar metal melts at a temperamm belowthe fusion and working, temperature of quartz. Invar metal is fluidbefore the quartz can be worked, and as a result it is not possible to'attain a seal between the two. similar expansion are known. Tungstenand molybdenum with expansion coefiicients of.

approximately 42x10 are the closest of the ,metals; and these twosubstances, in addition, have melting points substantially above theworking temperature for quartz.

Attempts have been made to fuse tungsten and molybdenum into quartz toproduce vacuum and gas tight seals. Thus in U. S. Patent No. 1,608,612,Nov. 30, .1926 is do- No other suitable substances of scribed a specialtreatment of molybdenum whlch enables it to be fused directly into thequartz. However, I found that according to the method described in theabove patent seals could be made vacuum tight provided only veryfinewires were employed. A seal which is capable'of carrying one and morea'mperes of current, such as required for the cury arcs. I have foundthat seals employing tungsten and quartz behave similarly to those withmolybdenum and no one has succeeded in producing seals which aresuitable for use with quartz mercury arcs and quartz discharge tubesthat consume currents ofone and more amperes. a

Attempts have also been made to provide a seal for tungsten andmolybdenum fused into quartz, the function of the seal being to make theunion between the quartz and the metal gas tight. Examples of theseseals are given in the catalogue of the Thermal Syndicate 1930 page 28.The sealing materials employed are lead or mercury. (See U. S. LettersPatents #1,118,812, Nov. 24, 1914 and #1,489,099, April 1, 1924.) Thelead seals introduce manufacturing difiiculties and are not very deendable in service.

Another form 0 metallic conductor that has been employed with somesuccess consists of a ground joint between the metal, usually invarmetal, and the quartz which is sealed by mercury. It hasbeen expensiveto manufacture and the number of failures have been high, due in a largepart to the solubility of air and water in mercury. and the subsequentpassage of a portion of this air and moisture does not withstand markedtemperature changes and high temperatures, and the number of failuresfrom these causes is high.

Still another form of metallic conductor which has been employedextensively on quartz mercury arcs consists of a metal sealed vacuumtight into a glass, which in turn is connected to the quartz by steps ofglass of decreasing coeflicient of thermal expansion until finally aglass step is reached that may be fused directly to the quartz. (See U.S. Patents 910,969; 1,014,757, Jan. 16, 1912; 1,191,630, July 18, 1916;1,154,081, Sept. 1915; 1,558,524 Oct. 27, 1925.) For example,tungstenmay be sealed vacuum tight to a commercial lead boro-silicateglass known as Nonex, having the coefficient of thermal expansion3.9x10, which in turn may be fused to pyrex with the coefiicient 3.2x10,which in turn may be fused to the special glasses described in the abovepatents. sitive to temperature changes, and the number of fractures atthe joints between the various glasses is-quite high.

It is an object of this invention to provide a'method of making vacuumtight and gas tight metallic conductors for use with quartz gas filleddevices, which conductors are inexpensive, durable, and capable ofwithstanding all temperature conditions to which such devices aresubjected.

A further object is the provision of a method for producing efficientmetallic conductors for use with gas tight and vacuum tight vaporelectric devices at a cost of manufaiplture lower than has heretoforebeen pos- S1 e.

These and other advantageous objects, which will later appear, areaccomplished by the simple and practical construction and arrangement ofparts hereinafter described in a sleeve '4 of fused quartz.

and exhibited in the accompanying drawing, forming part hereof, and inwhich The figure is a sectional view of a conductor made in accordancewith my invention.

Referring to the drawing, the conductor is shown to comprise a metalcore 3, enclosed The sleeve 4 fits the core very closely at the sectionindicated by the letter A, while at section B the sleeve is slightlyspaced from the core, and the space is filled with a compound 5hereinafter described.

The metal core 3 may be in the form of a bar, ribbon, rod or wire, thelatter, being the usual form. It is cleaned of oxide by any one of anumber of well known chemical or physical methods. The metals usuallyemployed as cores in my invention are tungsten, molybdenum, tantalum andplatinum, all of which melt at a temperature higher than the workingtemperature of fused quartz. My invention is not restricted to thesemetals as there may be alloys which have the physical Thesesealedconductors are quite sen-- characteristics suitable. for theconstruction of conductors in the manner described.

Another essential characteristic necessary for the successfulperformance of the metal conductor core 3 employed in my invention isthe coefficient of thermal ex ansion. Fused quartz has a very small coecient of thermal expansion, namely 0.6 x 10", and none of the abovementioned metals can be sealed vacuum tight. into quartz by fusion andat the same time be of sufficient cross section to conduct one or moreamperes of current in continuous duty because their coeflicients ofthermal expansion are considerably different from that of fused quartz.

I have constructed vacuum tight conductors employin the above metals andfused quartz that will carry as much as fifty amperes of current withoutdestruction. I am able to accomplish this provided the metal used has acoeiiicientof thermal expansion less than 9.0 x 10- and a melting pointhigh- 7 er than 1700 degrees centigrade, that is, higher than themelting point of fused quartz.

My method for accomplishing this will be described in detail. The metalcore 3 is first placed within the fused quartz sleeve 4. It is mostconvenient to have the sleeve fit quite closely, thus if the metal be inthe form of a wire 1 millimeter diameter, the bore can conveniently be1.25 millimeter. One end of the quartz sleeve 4 is closed by fusionbefore the metal is introduced or by means of a suitable stopper; thefirst method, fusion, being preferable. The other end of the sleeve isattached to. an evacuation pump, and the sleeve is evacuated. Thefunction of the vacuum is two fold. The removal of air is necessary inorder that the metal will not be oxidized durin subsequent heattreatment. The reduction in gas pressure within the quartz sleeveassists in the process of formin the quartz about the metal- This willnow he described.

The evacuated quartz sleeve containing the metal core is heated to theworkin temperature of fused quartz. This may ac complished by flames orelectrically. The quartz must be brought to a temperature of about 1650degrees centigrade. The portion of the sleeve which will be on theexternal,

. that is, the atmospheric side of the conextent than the quartz,andhence, will pull away from the quartz. The gap produced between themetal and the uartz will be greatest .on the external end of the con- 5ductor and the least on the end A to be attached to the gas'filledelectrical device.

The conductor is then removed fromvthe evacuating system, the closed endopened,

and the volatilized metal, if there be any,

cleaned out by acid or gentle glowing.

The conductor may be then attached to the quartz electrical device. Itis also prac-. tical in some instances to shrink the quartzsleeve aboutthe metal while attached to the main body. of the quartz electricaldevice, employing the procedure described above.

The metal core 3 is united, gas and moisture tight, to the'quartz sleeve4 by a compound which fills in part the gap between the metal core 3 andquartz sleeve, and which possesses physical properties that enable it tohermetically seal the metal to the quartz under all normal and operatingconditions.

I have found that compounds capable of being used in my conductor 'may'be prepared from mixtures of the higher hydrocarbons of the methane andbenzene series.

They must adhere firmly to both-the metal ing to a viscosity of about20,000 dyne-seconds per s uare centimeter.

The con uctor is warmed to about 300 debrought in contact therewith atwhich time 7 it melts and'flows about the metal, a portion passing intothe space between the metal and quartz of the sleeve. The conductor isthen cooled, and is ready for use.

From the above description it will be seen that I have provided a simpleand convenient method of making gas tight metallic" conductors for usein connection with gas filled fused quartz devices. While I havedescribed my method in detail, it is understood that I am not restrictedto the specific metals and compound set forth, as other metals andcompounds may possibly be used without departing from the spirit of theinvention set forth in the appended claims.

' Having thus described my invent-ion, what A I claim as new and'desireto secure by Letters Patent, is: 4 y

1. Themethod of constructing a metallic conductor for use on vacuum andgas-filled quartz electrical devices comprising, enclosing a metal corein a fused quartz sleeve having'a-bore of slightly greater diameter thanthe core, evacuating the sleeve, then vacuum heat treatingthe metal andsleeve to. cause the quartz to fit tightly about the metal core and thequartz, be elastic, and at 100 degrees centigrade should have afluidity.correspond-' grees 'centigrade and the compound is -isapproached and then introducing in the space between the core and thesleeve a compound which at 100 degrees centigrade has afluidity'corresponding to a viscosity of about 20,000 dyne-seconds persquare centimeter.

2. The method ofconstructing a metallic conductor for use on vacuum andgas filled quartz electrical devices, comprising placing a metal core inthe bore'of a fused quartz sleeve having a boreof slightly greaterdiameter than the core so that there is a substantially close fitbetween the core and sleeve, evacuating the sleeve, then vacuum heattreating the metal, and sleeve throughout their length, the intensity ofthe heat being gradually increased from one end of the sleeve to theother end to cause the quartz sleeve to fit tightly about the core atone end, and to be slightly spaced from the core throughout its length,the spacing graduaL,

1y increasing from one-end to the other, and then introducing in thespace between the core and sleeve a hydrocarbon compound to produce agas tight seal.

3. The method of constructing a metallic conductor for use on vacuum andgas filled quartz electrical devices, comprising placing a metal core inthe bore of a fused quartz sleeve having a bore of slightly greaterdiameter'than the core. so that there is a substantially close fitbetween the core and sleeve, evacuating the sleeve, then vacuum heattreating the metal and sleeve throughouttheir length, theintensity ofthe heat being gradually increased from one end of the sleeve to theother end to cause the quartz sleeve to fit tightly about the core atone end, and to be slightly spaced from the core throughout its length,the spacing gradually increasing from one end to the other, and

then introducing in the space between the February, 1932.

WILLIAM ANDERSON, JR.

at one end of the sleeveand -to be slightly spaced from the corethroughoutthe length 7 of the core in the sleeve, the spacing graduallyincreasing as the other end of the sleeve

